In both cases, this supporting information isn’t essential; it’s just nice to have.

There’s a potential performance problem though. Because this extra information is coming from third-party services—and despite the fact that I’m doing some caching—it could delay the display of the whole page. So I took some time on the weekend to adjust the architecture a little bit. Now the extra information is requested with Ajax once the core information has already loaded. This is lazy loading.

Now I’ve introduced a dependency on JavaScript, which is far from ideal, but because this is just “nice to have” information, I think it’s okay if it isn’t seen by a subset of visitors.

In fact, because this extra lazy-loaded stuff takes up valuable screen real estate, I think it might be acceptable to only serve it up to visitors who have the screen real estate to accommodate it:

if ($(document).width() > 640) {
// do lazy loading here
}

So if you load my profile on a small screen, you won’t see my latest tweets or my Last.fm recommendations. Likewise if you look at something I’ve huffduffed that’s tagged with music:artist=radiohead you won’t see information from Last.fm, pictures from Flickr or albums on Amazon unless you load the page with a wide enough viewport.

Lazy loading is the new fold

I was chatting with James about the implications that lazy loading could have for earlier phases of the design process: wireframing, page description diagrams, and so on.

Traditionally, you’ve got only two choices when judging what content to include: either something is on the page or it isn’t. You can use hierarchy, position and contrast to emphasise or de-emphasise the content but fundamentally, it’s a binary choice. But with conditional lazy-loading there’s a third option: include some content if the user’s circumstances warrant it.

Once again, Luke’s Mobile First approach is a useful thought experiment. It can help prioritise which elements are core content and which could be lazy-loaded:

Mobile devices require software development teams to focus on only the most important data and actions in an application. There simply isn’t room in a 320 by 480 pixel screen for extraneous, unnecessary elements. You have to prioritize.

So when a team designs mobile first, the end result is an experience focused on the key tasks users want to accomplish without the extraneous detours and general interface debris that litter today’s desktop-accessed Web sites. That’s good user experience and good for business.

Sometimes there are political reasons for wanting the “extraneous detours and general interface debris.” Lazy loading for large-screen users could be the least worst option in that situation. Semantically speaking, the kind of content that might be marked up in an aside element might be a good candidate for lazy loading …if the viewport is large enough.

I have a feeling that we’re going to be seeing a lot more of lazy loading as the responsive web design revolution rolls on. Used judiciously, it could provide plenty of performance benefits. But if it’s taken too far, lazy-loading could be disastrous, resulting in sites that rely on JavaScript to load their core content—I’m looking at you, Twitter.